使用 target name 而不是 _blank

[xjia1]

比如链接到某个题目，就用 <a href="..." target="problem_1234">

[webbrain-one]

Thanks for pointing this out! I opened a PR to fix #50: #60. It changes problem links to use a named target such as target="problem_1234" instead of target="_blank", so they open in the intended frame rather than a new tab.